1. Field of the Invention
The present invention is directed to a process and apparatus for comminuting particle rubber. More specifically, the present invention is directed to a process and apparatus for comminuting a used rubber particle feedstock to produce powder rubber sized particles.
2. Background of the Prior Art
The disposal of used tires and other rubber articles has long been a major environmental concern insofar as the large number of used tires overwhelm waste disposal sites. Furthermore, indiscriminate discarding of tires and other rubber articles create unsightly environmental problems. It is for this reason that processes have been developed to dispose of tires in a manner that not only eliminates them as an environmental problem but provides incentives for commercialization of tire disposal processes.
Independent of the process employed most such processes includes the step of rubber comminution in which rubber particles of relatively large size are reduced to sizes that can be reused in new rubber articles including new vehicle tires. These commercially useful used rubber grades include crumb and powder rubber.
Rubber comminution processes and apparatus must overcome an inherent physical property characteristics of rubber, its high degree of elasticity. Thus, rubber, at ambient conditions, is very difficult to comminute. In order to overcome this difficulty processes and apparatus have been developed to reduce the temperature of the rubber to reduce its elasticity. To obtain fine particle sized rubber it is often required to reduce rubber particles to below its glass transition temperature. At temperatured below the glass transition temperature the rubber becomes a brittle vitreous material.
Although processes and apparatus for comminuting rubber are known in the art wherein the rubber particles are chilled to below the glass transition temperature, problems associated with comminuting rubber are still present in such processes and apparatus. One of the problems associated with comminuting rubber is the temperature rise associated with this activity. Thus, the rubber may be at its glass transition temperature upon entering the comminuting apparatus but, due to frictional forces during comminution, the temperature of the rubber rises above the glass transition temperature resulting in the re-emergence of elastic properties which prevents complete comminuting efficiency.
Another problem associated with processes and apparatus for comminuting rubber in the prior art is the variability of the rubber employed. That is, the rubber particles entering a mill are not homogeneous. Rubber particle lots may vary in average particle size and other physical characteristics requiring variation in comminution to produce a uniform powder rubber particle size.
As stated above, the prior art discloses processes and apparatus for comminuting rubber particles. Among the more pertinent of these disclosures is U.S. Pat. No. 5,588,600. The '600 patent describes a process and apparatus for low temperature comminution of tires in which cryogenic fluids, employed in embrittling rubber particles so that comminution can effectively occur, is recycled. This process produces crumb and powder rubber of sufficiently small particle size useful in the production of new vehicle tires and other rubber products.
U.S. Pat. Nos. 5,368,240 and 4,863,106 describe processes and apparatus for reducing rubber to fine particle sizes. Although both of these disclosures describe processes for producing fine-sized rubber using cryogenic fluids, neither of these references disclose means for custom designing the particle size range of the product to enhance commercial reliability of those processes.
The disclosure of a grinding means in U.S. patent application Ser. No. 10/714,782, filed Nov. 17, 2003, assigned to the assignee of the present application, which application is incorporated wherein by reference, discloses a grinding means which overcomes some of the problems associated with the prior art comminution of rubber particles. However, even that grinding means, denoted in the aforementioned application at 20, does not overcome some of the problems associated in the prior art with grinding processes and apparatus.
The above remarks establish the need in the art for a new process and apparatus for comminuting rubber particles to produce commercially viable powder rubber. Such a process and apparatus is necessary to overcome problems associated with rising temperatures in the comminuting processes and apparatus of the prior art and better accommodates production of these products in spite of varying rubber particle size feedstocks.